The invention relates to an energy storage device comprising a high pressure liquid accumulator, a low pressure liquid accumulator and at least one pump and motor unit, i.e. a device able to be used as a pump and a motor which is connected to a means supplying or absorbing energy as the case may demand and during charging of the high pressure lator functions as a pump and on discharge thereof functions as a motor, at least that pressure line connecting the high pressure accumulator and the pump and motor unit having a shut off valve therein.
In the prior art, see for example the German patlator functions as a pump and on discharge thereof functions as a motor, at least that pressure line connecting the high pressure accumulator and the pump and motor unit having a shut off valve therein.
In the prior art, see for example the German Pat. No. 2,904,572, low pressure liquid accumulators have so far been used, in which during discharge the pressure sinks relatively sharply from a maximum to a relatively low pressure. In the case of high flow rates this leads to cavitation and possibly to an overly low operating pressure. The design and workings of such liquid accumulators are described for example in the German periodical "Der Konstrukteur", 12/1984, pages 51 through 59.